Integrated device providing current-regulated charge pump driver with capacitor-proportional current

ABSTRACT

An integrated circuit regulates current flowing from a battery to a load without requiring an external current sense resistor. The IC includes a primary charge pump; a model charge pump; a current sense circuit, a first control circuit to force a voltage level at the output of the model charge pump to be equal to a voltage level at the output of the primary charge pump; and, a second control circuit to force a model current put out by the model charge pump to be equal to a reference current. Current passing through the primary charge pump is regulated at a level established by the capacitance value of an external flying capacitor irrespective of input voltage variation of the battery power source.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention relates to integrated circuit components adaptedto surface mount technology. More particularly, the present inventionrelates to an integrated circuit including a current regulated chargepump wherein the magnitude of the output current is adjusted via scalingof a single external charge pump capacitor.

Introduction to the Invention

Battery operated appliances have proliferated throughout the world. Cellphone handsets, portable radios and playback units, personal digitalassistants, light emitting diode (LED) flashlights, and wirelesssecurity and remote control systems provide only a few of many examplesof such appliances. Small batteries of the types commonly employed inthese appliances typically do not put out either constant current orconstant voltage. In order for output loads, such as LEDs to be suppliedwith constant current, feedback regulation techniques are employed.Regulation may be as simple as a ballast resistor or as complex as anintegrated circuit with feedback control.

LEDs typically require a supply voltage potential which frequentlyexceeds the voltage potential supplied by a particular cell or lowvoltage battery. For example, white LEDs have a forward voltage of 3.5volts typical, and 4.0 volts maximum, at a current of 20 milliamperes(mA), whereas a single-cell lithium battery delivers approximately 3.6volts and two alkaline cells in series deliver approximately 3.0 volts.In this circumstance, a voltage converter is typically employed to boostthe voltage to a level suitable for supplying the LED.

One example of a known integrated circuit boost converter IC1 is givenin FIG. 1. In this example, the boost converter IC1 may be a type RYC9901 high-power multi-LED boost converter supplied by Tyco ElectronicsCorporation, the assignee of the present invention, or equivalent. Thiscircuit IC1 may be operated from a battery B comprising a single lithiumcell or two alkaline cells in series, and is capable of driving up to 8LEDs in series, two LEDs D1 and D2 being shown in FIG. 1. In normaloperation, IC1 operates as a discontinuous conduction mode non-isolatedflyback converter.

When an NMOS transistor switch M1 is conducting, current from battery Bflows into an external inductor L1 and a magnetic field develops. Whenthe switch M1 is turned off, current flows out of the inductor, throughan external Schottky diode SD1 and into a storage capacitor C2. When thestorage capacitor C2 is charged, current at a higher voltage thansupplied from the battery B passes through one or more series-connectedlight emitting diodes D1, D2 and a current sense resistor R1 providing afeedback control signal to IC1. An input filter capacitor C1 may beprovided. As shown in FIG. 1, IC1 may also include internal elementsincluding amplifiers U1 and U2, AND gate GI, latch LA1 and an internalcurrent sense resistor R2, connected as shown.

Another known way to generate constant current for a load, such as anLED, is to employ a charge pump circuit topology. For example, a typeMAX684 voltage regulated charge pump, supplied by Maxim IntegratedProducts, Inc., Sunnyvale, Calif., can power three or more white colorLEDs. The MAX684 charge pump regulator generates 5 volts from a 2.7V to4.2V input, but requires a ballast resistor or current source for eachLED as well as external capacitors. The ballast resistors lower theefficiency of the driver by the large voltage drop needed. In order tocontrol brightness, Maxim suggests that an external switching transistorcontrolled by a PWM brightness control be employed.

With reference to FIG. 2A, a single charge pump voltage doubler/inverterrepresentative of the prior art is shown. A DC voltage applied acrossterminals 1 and 2 becomes stored in an input charge store, such ascapacitor Ci. When switches S1 and S2 are closed, the charge istransferred from input capacitor Ci to a so-called “flying” capacitor Cfin accordance with a current flow Ia. Switches S1 and S2 are opened, anda potential now appears across the flying capacitor Cf. Then, switchesS3 and S4 are closed, and the charge across the flying capacitor Cf istransferred to an output charge store, such as capacitor Co. Switches S3and S4 are opened, and the charge across the output store Co isavailable to be supplied to a load. It is important to the properoperation of the charge pump shown in FIG. 2A that the switch pairsS1-S2 and S3-S4 are closed during non-overlapping clock intervals.Accordingly, a clock circuit generates a first switch phase PHI 1(applied to control S1 and S2) and a second, non-overlapping switchphase PHI 2 (applied to control S3 and S4) as shown in FIG. 2B. (Inpractice actual clock non-overlap is less than as graphed in FIG. 2B.)If terminal 4 is connected to terminal 1, a voltage doubler results. Ifterminal 3 is connected to terminal 2, a voltage inverter results. Whenthe switches S1, S2, S3 and S4 are true MOS switches, they permitcurrent to flow in either direction when closed, thereby allowing energytransfer from output to input as well as from input to output. Whilethis prior topology has worked satisfactorily, like the FIG. 1inductor-based solution, the prior charge pump solution has typicallyrequired an external sense resistor to regulate and maintain a constantcurrent flow through the external load.

A hitherto unsolved need has arisen to provide a single, integratedcircuit driver which uses a charge pump topology in which magnitude ofoutput current to a load is adjusted by the scaling of capacitance of asingle external flying capacitor and maintained at the scaled level, ina manner overcoming limitations and drawbacks of the prior art.

BRIEF SUMMARY OF THE INVENTION

A general object of the present invention is to provide an electroniccircuit for driving a load with a constant current irrespective ofvariations in supply voltage within a supply voltage range.

Another object of the present invention is to provide an electroniccircuit comprising a current regulated charge pump wherein magnitude ofoutput current is established by selecting the value of an externalflying capacitor.

Yet another object of the present invention is to provide an electronicdriver circuit for delivering a constant output current over a range ofinput voltage, based upon a dual charge pump circuit topology enablingcomparison of a model charge pump current set by an internal flyingcapacitor with output current put out by a primary charge pump, suchthat regulated output current is set by selecting the value of anexternal flying capacitor within the primary charge pump circuitarrangement.

Still one more object of the present invention is to provide a low-cost,high frequency charge pump integrated circuit for driving one to foursuper-bright LEDs, for example, with a constant current over an inputvoltage range usually present with battery power supplies and withoutneed for any external current sense resistor.

Yet one more object of the present invention is to provide a low-costsix-pin current regulated charge pump driver IC with external enable anduser settable regulated drive current, which can be fabricated usingknown low-cost CMOS IC processes.

As one aspect of the present invention, an electrical system is providedfor regulating electrical current flowing from a power source to a load.In this particular aspect, the electrical system includes the followinginterconnected structural elements. A current pass regulator element isconnectable to the power source and functions to control supply currentdrawn from the power source. A primary voltage multiplying finite outputresistance circuit has an input connected to the current pass regulatorelement and an output connectable to the load. The primary voltagemultiplying finite output resistance circuit includes a user settableoutput resistance determining element for determining magnitude ofoutput resistance. In a preferred embodiment, the current determiningelement comprises a flying capacitor within a primary charge pumpcircuit. A model voltage multiplying finite output resistance circuitincludes an input connected to the current pass regulator element andprovides an output to a current sense circuit that supplies an outputcurrent equal to model voltage multiplying circuit output current(Imodel). A constant current source sinking a reference current (Iref)is connected to the current sense output. The current sense circuitforces the output of the model voltage multiplying circuit to be equalto the primary voltage multiplying circuit output. Thus, both theprimary and model voltage multiplying circuits enjoy the same terminalvoltages, or operating point. Therefore, the ratio of the primaryvoltage multiplying circuit output current to the model voltagemultiplying circuit output current is fixed by the multiplying circuitdesigns, and not by the terminal voltages. In a preferred embodiment,this ratio is established as a ratio between capacitance of an internalcapacitor to capacitance of an external capacitor. A control circuitcontrols the current pass regulator element to force the current Imodelto be equal to the reference current Iref. In this manner currentpassing through the primary voltage multiplying finite output resistancecircuit is regulated at a level established by the user settable currentdetermining element irrespective of input voltage variation of the powersource. A related aspect of the present invention provides an integratedcircuit for regulating electrical current flowing from a battery powersource to a load without requiring an external or internal current senseresistor. This related aspect is realized by using a model charge pumpthat “mirrors” the primary charge pump to generate a scaled copy of theoutput current. The two charge pumps are controlled in unison, so thatthe scaled model current is fixed by an internal current reference.Thus, the primary charge pump output current is stabilized without anysense resistor.

As a further aspect of the present invention, a method is provided forregulating current flowing from a battery to a load without directlysensing current flow at the load. In this aspect of the presentinvention, the method includes the following steps:

-   -   (a) passing current from the battery through a current pass        regulator element,    -   (b) providing current from the current pass regulator element to        a primary voltage multiplying finite output resistance circuit        providing current flow to the load,    -   (c) selecting a value for a user settable output resistance        determining element of the primary voltage multiplying finite        output resistance circuit in order to determine magnitude of        regulated current to flow to the load,    -   (d) providing current from the current pass regulator element to        a model voltage multiplying finite output resistance circuit in        order to generate a model current Imodel,    -   (e) passing the model current through a current sense element,        and into a constant current source for sinking a reference        current Iref, and    -   (f) controlling the current pass regulator element to force the        current Imodel to be equal to the reference current Iref, such        that current passing through the primary voltage multiplying        finite output resistance circuit is regulated at a level        established by the user settable current determining element        irrespective of input voltage variation of the power source.

These and other objects, advantages, aspects and features of the presentinvention will be more fully understood and appreciated uponconsideration of the detailed description of preferred embodimentspresented in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block and schematic circuit diagram of a conventionalintegrated circuit boost converter for driving a load to a current levelmonitored by an external resistor and feedback connection.

FIG. 2A is a simplified schematic circuit diagram of a capacitor-basedcharge pump known in the prior art.

FIG. 2B is a graph of two-phase clock waveforms drawn along a commonhorizontal time base.

FIG. 3 is a block and schematic circuit diagram of an integrated circuitforming a charge pump driver for a load in accordance with principles ofthe present invention.

FIG. 4 is a more detailed diagram illustrating the primary charge pumparchitecture and clock included within the FIG. 3 block and schematiccircuit diagram.

FIG. 5 is a greatly enlarged top plan view of a miniature surface-mountintegrated circuit package including the FIG. 3 IC circuitry inaccordance with principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with principles of the present invention, and as shown inthe circuit of FIG. 3, an integrated circuit 10 implements a currentregulated charge pump wherein the magnitude of output current isadjustable by scaling of the capacitance value of a single externalflying capacitor Cp. The IC 10 includes two charge pumps, namely aprimary charge pump 12 and a model charge pump 14. While the primarycharge pump 12 may have any switching topology, it most preferably is inaccordance with the FIG. 4 arrangement, having internal connections toform a voltage doubler. While the circuit topology must be the same forboth the primary charge pump 12 and the model charge pump 14, the actualcircuit layouts may be scaled so long as the primary charge pump 12operates proportionally with respect to the model charge pump 14, withthe nominal current put out by the primary charge pump 12 being set by auser-selected, externally connected flying capacitor Cp. By making theprimary charge pump 12 electrically proportional to the model chargepump 14, the model charge pump 14 can be operated at far less currentthan that used and sourced by the primary charge pump 12, and take upfar less integrated circuit die area.

The primary charge pump 12 utilizes the externally connected capacitorCp as its flying capacitor, whereas the model charge pump 14 utilizes aninternal capacitor Cm formed on the integrated circuit chip as itsflying capacitor. The primary charge pump 12 has an output V1 that formsthe OUT path for the IC 10. The model charge pump 14 has an output V2. Avoltage amplifier U3 (having finite gain) subtracts the V2 output fromthe V1 output to provide a difference voltage. The circuit U3 may beimplemented in a variety of manners including, but not limited to, anoperational amplifier or a PMOS differential pair. The differencevoltage put out by U3 is applied to a control gate electrode of a PMOStransistor M2. The PMOS transistor M2 is connected in series between themodel charge pump output V2 and a constant current source 16 that sinksa constant current Iref to ground. The circuit elements U3 and M2 form acurrent sense circuit that forces V2 to be approximately the same as theoutput voltage on OUT. The current required to achieve this is Imodel,the output current from the model charge pump 14.

A series pass regulator element, represented in the FIG. 3 block diagramas a PMOS transistor M3, is provided to adjust the input drive levelfrom a DC supply 18, such as a lithium battery, to the primary chargepump 12 and the model charge pump 14. An input capacitor C3 minimizesvoltage drops at the input of the IC 10 in response to high frequencyswitching operations occurring within the charge pumps 12 and 14. Anoutput capacitor C4 acts to filter out any switching transientsotherwise remaining in the output current supplied by IC 10.

A current controlled voltage source U4 has an input connected to a nodebetween the drain electrode of PMOS transistor M2 and the constantcurrent source 16, and has an output connected to a gate controlelectrode of the pass element PMOS transistor M3. The circuit U4functions as a current-to-voltage converter and generates a voltagecontrol as a function of current imbalance between Imodel and Irefsensed at its input. The voltage control is applied to a control gateelectrode of the pass element M3 such that the current Imodel passingthrough the PMOS transistor M2 is forced to remain equal to the internalfixed reference current Iref generated by constant current source 16. IfImodel is greater than Iref, excess current present at the input of U4is sinked to ground through U4 and the voltage control to M3 causesinput current to be reduced. If Imodel is less than Iref, additionalcurrent is sourced by U4 to the constant current source 16 and thevoltage control to M3 causes input current to the charge pumps to beincreased. This regulation process operates automatically to maintainImodel equal to Iref.

The integrated circuit 10 includes an internal clock element 20 whichgenerates the non-overlapping switching signals Phi 1 (i.e. Φ1) and Phi2 (i.e. Φ2) shown in FIG. 2B at a suitable clock frequency, such as 1.2MHz for example, and applies them simultaneously to control the primarycharge pump 12 and the model charge pump 14. A true logical level at theenable pin EN of IC 10 enables the circuitry to generate and put outregulated current lout to a load 22. The load may be any desired load,particularly but not necessarily one or more super-bright LEDs. A lowfrequency pulse width modulator (PWM) signal applied to the enable pinEN turns the IC 10 on and off, thereby modulating the output current anddimming the LED light level, for example. For example, applying a 1 KHzPWM signal with a duty cycle of 700 microseconds results in a lightlevel which is 70% of the maximum drive level set by the externalswitched capacitor Cp.

Multiple LEDs may be connected in series or in parallel. If connected inparallel, current equalization series resistors or ballast resistors maybe utilized to balance current flows and light outputs of the multipleLEDs, given a range of manufacturing tolerances. If several super-brightLEDs are to be driven, output light level matching considerations mayrequire small ballast resistors. These resistors can typically besmaller and more efficient than the fixed output voltage designtechniques employed in the prior art discussed hereinabove. For example,FIG. 5 shows four super-bright LEDs D10, D11, D12, and D13, each LEDhaving a series current equalization resistor R10, R11, R12 and R13selected to make light output of diodes D1-D4 uniform.

Since the input voltage Vreg output by the pass element PMOS transistorM3 is common to both the primary charge pump 12 and the model chargepump 14, and the output voltages of both charge pumps are forced to beequal, the output current produced by the model charge pump 14 is ascaled replica of the output current produced by the primary charge pump12. The output current lout can be expressed as follows:${Iout} = {\frac{Cp}{Cm}{Imodel}}$

Since the circuit U4 forces the current Imodel to be equal to thereference current Iref, the output current can be expressed as follows:${Iout} = {{\frac{Cp}{Cm}{Iref}} = {CpK}}$

Since the constant K is fixed by appropriate design of the integratedcircuit 10, the regulated output current lout can be scaled by selectingthe capacitance value of the external flying capacitor Cp. In normaloperation, the IC 10 delivers a constant current to the load, regardlessof actual input voltage within an operational range.

For example, over an input voltage range of 1.6 to 3.4 volts, a 100nanofarad (nF) capacitor Cp results in approximately 30 mA of outputcurrent, a 47 nF capacitor Cp results in approximately 20 mA of outputcurrent, a 22 nF capacitor results in approximately 15 mA of outputcurrent, and a 10 nF capacitor results in approximately 5 mA of outputcurrent, from IC 10. With a switching frequency of 1.2 MHz, full currentis reached in approximately four microseconds from first assertion ofthe enable signal.

IC 10 is most preferably fabricated using known low-cost CMOS ICprocesses. As shown in FIG. 5, IC 10 may be contained in a small packagehaving only six external pins: Cp1 (pin 1), ground (pin 2), enable (pin3), Vin (pin 4), OUT (pin 5) and Cp2 (pin 6). Preferably, although notnecessarily, the package may comprise an industry standard surface-mountSOT-23-6 package having a nominal length of 3.0 mm, a width (exclusiveof pins) of 1.67 mm and a height of 1.35 mm, for example. With thearrangement shown, there is no need for, nor provision for, any externalsense resistor or pin therefor.

Thus, it will be appreciated that the present invention provides acharge pump based driver integrated circuit 10 providing constantcurrent regulation, user settable by selection of an external flyingcapacitance value, with a wide current range extending to 100 mA, ormore. The circuit 10 operates with a wide input voltage range, forexample 1.6 volts to 5.0 volts. When non-enabled in shutdown mode, thecircuit 10 draws as little as 2 μA. The circuit 10 enable may be pulsewidth modulated so as to provide a ten to one linear dimming range forLEDs. Applications for the integrated circuit 10 include, but areclearly not limited to, driving super-bright LED flashlights,battery-powered indicator lights, cell phone display panel backlighting, keyless entry systems, wireless security systems, automaticmeter readers, etc.

Having thus described a preferred embodiment of the invention, it willnow be appreciated that the objects of the invention have been fullyachieved, and it will be understood by those skilled in the art thatmany changes in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. Therefore, the disclosuresand descriptions herein are purely illustrative and are not intended tobe in any sense limiting.

1. An electrical system for regulating electrical current flowing from apower source to a load, the electrical system comprising: (a) a currentpass regulator element connectable to the power source to control supplycurrent drawn from the power source, (b) a primary voltage multiplyingfinite output resistance circuit having an input connected to thecurrent pass regulator element and an output connectable to the load,and having a user settable regulated current determining element fordetermining magnitude of regulated current to flow to the load, (c) amodel voltage multiplying finite output resistance circuit including aninput connected to the current pass regulator element and an outputsupplying a model current Imodel, (d) a current sense circuit connectedto force an output voltage of the model voltage multiplying finiteoutput resistance circuit to be equal to an output voltage of theprimary voltage multiplying finite output resistance circuit, (e) aconstant current source for sinking a reference current Iref, and (f) acontrol circuit responsive to the current sense circuit and the constantcurrent source and connected to control the current pass regulatorelement to force the model current Imodel to be equal to the referencecurrent Iref, such that current passing through the primary voltagemultiplying finite output resistance circuit is regulated at a levelestablished by the user settable current determining elementirrespective of input voltage variation of the power source.
 2. Theelectrical system set forth in claim 1 including a non-overlapping twophase clock generator and wherein the primary voltage multiplying finiteoutput resistance circuit comprises a first charge pump clocked by theclock generator and wherein the user settable regulated currentdetermining element comprises a flying capacitor having a capacitancevalue selected by the user to establish regulated output current level.3. The electrical system set forth in claim 2 wherein the model voltagemultiplying finite output resistance circuit comprises a second chargepump clocked in synchronism with the first charge pump.
 4. Theelectrical system set forth in claim 3 wherein the current sense circuitcomprises a voltage comparison circuit having a first input connected tomonitor output voltage of the primary voltage multiplying finite outputresistance circuit, having a second input connected to monitor outputvoltage of the model voltage multiplying finite output resistancecircuit, and having a voltage comparison output; and, a model currentregulator responsive to the voltage comparison output and connected toforce the output voltage of the model voltage multiplying finite outputresistance circuit to be equal to the output voltage of the primaryvoltage multiplying finite output resistance circuit.
 5. The electricalsystem set forth in claim 4 wherein the model current regulator of thecurrent sense circuit is connected in series with the constant currentsource, and wherein the control circuit comprises a current controlledsource having an input connection to a node between the model currentregulator and the constant current source for sourcing and sinkingcurrent to maintain model current Imodel equal to reference current Irefand having an output connected to control current passing through thecurrent pass regulator element.
 6. The electrical system set forth inclaim 5 wherein the current pass regulator element comprises a voltagecontrolled current regulator, and wherein the current controlled sourcecomprises a current controlled voltage source for outputting a voltagecontrol.
 7. The electrical system set forth in claim 4 wherein the modelcurrent regulator comprises a metal oxide semiconductor field effecttransistor.
 8. The electrical system set forth in claim 6 wherein thevoltage controlled current regulator comprises a metal oxidesemiconductor field effect transistor.
 9. The electrical system setforth in claim 1 formed as a monolithic integrated circuit chip withoutthe user settable regulated current determining element and havingexternal connections to the power source, load and user settableregulated current determining element.
 10. The electrical system setforth in claim 9 having an additional external connection to an enablesignal.
 11. The electrical system set forth in claim 9 contained in asix-pin integrated circuit package comprising a power source pin, aground return pin, a load pin, an enable pin, and two pins forconnecting the user settable regulated current determining element. 12.The electrical system set forth in claim 11 wherein the package conformsto an industry-standard SOT-23 package convention.
 13. The electricalsystem set forth in claim 1 wherein the power source comprises a batteryand the load comprises at least one light emitting diode.
 14. Anintegrated circuit formed in accordance with a complementary metal oxidesilicon process for regulating electrical current flowing from a batterypower source to a load without requiring an external current senseresistor, the integrated circuit comprising: (a) a current passregulator element connectable to the battery power source to controlsupply current drawn from the power source, (b) a primary charge pumphaving an input connected to the current pass regulator element and anoutput connectable to the load, and having pin connections to anexternal flying capacitor, the value of the external flying capacitorselected to fix magnitude of regulated current to flow to the load, (c)a model charge pump having an input connected to the current passregulator element and a model output supplying a model current Imodel,and including a current sense circuit, and a constant current source forsinking a reference current Iref, wherein the current sense circuit isconnected and functions to compare voltage levels at the outputs of theprimary and model charge pumps and to force voltage level at the outputof the model charge pump to be equal to a voltage level at the output ofthe primary charge pump, and (d) a control circuit having a currentsourcing/sinking input connected to a node between the current sensecircuit and the constant current source and having a control outputconnected to control the current pass regulator element to force thecurrent Imodel to be equal to the reference current Iref, such thatcurrent passing through the primary charge pump is regulated at a levelestablished by the capacitance value of the flying capacitorirrespective of voltage variation of the battery power source.
 15. Theintegrated circuit set forth in claim 14 wherein the current passregulator element comprises a voltage controlled current regulator, andwherein the control circuit comprises a current controlled voltagesource for outputting a voltage control to control the voltagecontrolled current regulator.
 16. The integrated circuit set forth inclaim 14 contained in a six-pin integrated circuit package including apower source pin, a ground return pin, a load pin, an enable pin, andtwo pins for connecting the external flying capacitor.
 17. Theintegrated circuit set forth in claim 15 wherein the package conforms toan industry-standard SOT-23 package convention.
 18. The integratedcircuit set forth in claim 14 wherein the load comprises at least onelight emitting diode.
 19. A method for regulating current flowing from abattery to a load without directly sensing current flow at the load,comprising the steps of: (a) passing current from the battery through acurrent pass regulator element, (b) providing current from the currentpass regulator element to a primary voltage multiplying finite outputresistance circuit providing regulated current flow to the load, (c)selecting a value for a user settable output resistance determiningelement of the primary voltage multiplying finite output resistancecircuit in order to determine magnitude of regulated current to flow tothe load, (d) providing current from the current pass regulator elementto a model voltage multiplying finite output resistance circuit in orderto generate a model current Imodel, (e) passing the model currentthrough a current sense circuit, and into a constant current source forsinking a reference current Iref, (f) controlling the current sensecircuit to force a voltage level at the output of the model voltagemultiplying finite output resistance circuit to be equal to a voltagelevel at the output of the primary voltage multiplying finite outputresistance circuit, and, (g) controlling the current pass regulatorelement to force the current Imodel to be equal to the reference currentIref, such that current passing through the primary voltage multiplyingfinite output resistance circuit is regulated at a level established bythe user settable current determining element irrespective of inputvoltage variation of the power source.
 20. The method set forth in claim19 wherein the step of providing current from the current pass regulatorelement to a primary voltage multiplying finite output resistancecircuit comprises providing current to a primary charge pump, whereinthe step of providing current from the current pass regulator element toa model voltage multiplying finite output resistance circuit comprisesproviding current to a model charge pump, and wherein the step ofselecting a value for a user settable output resistance determiningelement comprises selecting a capacitance value of an external flyingcapacitor in order to determine magnitude of regulated current flow tothe load.
 21. The method set forth in claim 19 for regulating currentflowing to a load comprising at least one light emitting diode.